Production of paper pulp



Sept. 5, 1961 Filed Aug. 2, 1955 3 Sheets-Sheet l woon am s HOT WATER 3 l6 ix/ g] BLOW z; 22 TANK BROWN STOCK CHEST J6 J7 .70 [Z ja- LIQUOR MEASURING TANK t 40 4/ X47 .7] -34 0/54 45 u: 44 J! 46 OXIDATION CONG- EVAR EVAI? EVAP. TOWER cowc. BLACK BLACK LIQUOR 4] LIQUOR STORAGE 5:- RECDVERY L as SYSTEM p 152 Z7 U /Z 32 J W 38' j J/ x V396, 5 7% Z 4 F 4/ LIQUOR C T L MEASURING 46R TANK OXIDATION ,4: i TOWER v49 3 EVAB EVA}? EVAP l I T cowc CONC. INVENTOR.

BLACK BLACK E mo/v Tum/w (om/vs, J2. LlQUOR LIQUOR B RECOVERY STORAGE SYSTEM Hfi-MN A TT ORNE Y Sept. 5, 1961 T. T. COLLINS, JR

PRODUCTION OF PAPER PULP Filed Aug. 2, 1955 3 Sheets-Sheet 2 OXIDATION TOWER OXIDIZER TANK EVAE EVAP. COM EVAP BLACK LIQUOR STORAGE Y TANK FOR TALLOIL PLANT EV F. cowc. A BLACK LIQUOR STORAGE Y EVAP EVAR

0X1 DATTON TOWER INVENTOR. Z9590 7/: FORD [mu/vs, JR.

A TTORNEY Sept 1961 T. T. COLLINS, JR 2,999,044

PRODUCTION OF PAPER PULP Filed Aug. 2, 1955 3 Sheets-Sheet 3 WOOD CHIPS 5 HOT WATER I l j .7]

BLOW TANK EVAR EVAP. OXIDATION EVAR TOWER /Zl/ lip/oz 96; 29 971 m INVENTOR. (P; THEM/v Tum/e0 [cu/N5, JR.

B am a??? 6' AUORNEY V LIQUOR 26 88 *MEASURING 87 P P L TANK 93 66 United States Patent C) Filed Aug. 2, E55, Ser. No. 525,883 Claims. (Cl. 162-30) My invention pertains to processes for the production of kraft paper pulp from southern pine andlike woods, and particularly pertains to black liquor utilization and treatment in such systems.

A general object of my invention is to improve the processes of producing pulp from southern pine and like woods, and a specific object is to provide a process for such pulp production which will make more practical the inclusion of a black liquor oxidation step in the process.

A representative system for the production of kraft paper or paperboard from southern pine woods includes the steps of chipping, cooking in digesters with steam, white and black liquor, defibering with Claflin or Jordan machines or the like, washing in a series of brown-stock washers wherein the pulp flows from stage to stage while the washing liquid, hot water in the final stage, flows in the reverse direction, Washing the pulp in each stage and becoming black liquor of about 16% solids in the first stage, and finally the provision of the washed pulp to screens, refiners and the Fourdrinier machine. The black liquor from the first stage is used in two ways, it is fed as dilution liquor to preliminary pulp treatment means, including the digester, the blow tank and to the pulp immediately prior to introduction thereof into the first washer stage, and it isv concentrated and burned to recover sulphur and other valuable chemicals. it is known in such systems, as suggested by'U.S. Patent No. 2,570,- 460 to, Otto Kress and No. 2,593,503 to G. H. Tomlinson et al. to oxidize the black liquor collected from the first stage washer prior to concentration thereof in vacuum evaporators, and it is particularly to systems wherein such oxidation of black liquor is included as a process step that-this invention pertains.

A persistent problem in the processing of southern pine and like woods is the occurrence of fatty and resin acid soaps in the black liquor. As used herein, southern pine and like woods will be understood to include slash pine; of the southern United States and similar highly resinous woods of the type which may be processed by the sulphate process into kraft paper and paperboard.

"It has been recognized that the dilution liquor returned to the preliminary treatment portions of the system, and by preliminary treatment it is intended to refer to portions of the system preceding the brown-stock washers, should be as soap-free as practicable because soap carried by the pulp into the final washer or washers may precipitate andclog the screens of the washers and paper machine.

Soap also causes trouble in oxidizing towers, since its presence results in increased foam production. It is further desired to extract as much soap as possible prior to burning of the black liquor to recover the chemicals therein, for example, as tall oil. It has been the practice, accordingly, to skim soap appearing on the surface of the black liquor in a tank interposed between two of the series-connected evaporation-units of the evaporator or concentration system. It has been found that black liquor of about 26% solids content, or between about 23 and 28%, can holdin' solution a minimum concent-ration of soap. Accordingly the soap is normally skimmed from liquor having about this percentage of solids.

An object of my invention is to reduce the amount of soap in the black liquor which is used as dilution liquor in the preliminary treatment steps. It is a further object of my invention to reduce the deposits of soap which "ice 2 have heretofore required periodic cleaning of the first stage filtration tank, the oxidation tower, and other tanks which may be employed in the storage and treatment of black liquor.

in the handling of black liquor, foam inevitably occurs in tanks and towers in which black liquor is present. It is usual practice to provide foam breakers at or near the tops of such tanks and towers, which foam breakers typically comprise a motor driving some sort of rotatable blades, paddles or similar elements which throw heavy liquid particles outwardly, breaking the bubbles and permitting the escape of the entrapped air or gas. The output of such foam breakers comprises a vapor, which is normally permitted to escape into the atmosphere, and a liquid phase comprising what may be termed partially broken foam. While some portion of this liquid phase may comprise liquid without entrapped gas, the major portion normally comprises a thin or soapy foam with bubbles of entrapped air or gas.

It has been found that return of the foam breaker liquid output, as distinguished from the vapor output, to the tank from which the foam is supplied to the foam breaker results, apparently, in the recirculation of the portions of the output which still contains gas or air bubbles and much of the foam breaker return becomes, after several passes, homogenized into a thick mayonnaise or very thick soup. This mayonnaise is difiicult to remove from the tank and may eventually substantially fill the tank. Being soap-rich, the mayonnaise is highly objectionable in the dilution liquor and in oxidation towers and concentrators.

It is a further object of my invention to minimize the production of mayonnaise and to isolate such mayonnaise as may be formed from the dilution liquor and from the oxidation tower.

The objects of my invention are accomplished, in gen-' eral, by supplying liquid and partially broken foam from the first stage filtrate tank to a second tank, rather. than returning the liquid output to the filtrate tank; by continuously skimming the surface of the liquid in the first stage filtrate tank and preferably supplying the soap, liquor and foam so skimmed to the second tank, and, according to the preferred embodiment, by mixing sufficient concentrated black liquor with the liquor extracted from the filtrate tank to bring up the solids content of the liquor in the second tank to between about 23 and 28 percent. The soap which forms on the liquor surface in the second tank is skimmed off and discarded or placed in a set-. tling tank, the foam above the liquor in the second tank is removed, either by being permitted to spill over the top of the tank, by being passed through a foam breaker, or by being sucked out through the soap skimmer, and the foam may also be discarded or added to the settling tank, and the approximately 26 percent liquor is removed below the surface of the liquor and is fed to the oxidizing tower,

Since black liquor having approximately 26% solids dis solves or entrains'the minimum percentage of soap, and since the soap-rich phases in the second tank are being constantly withdrawn therefrom, the liquor fed to the oxidation tower is substantially soap free. This system, accordingly, contributes a further advantage derivable from this invention in permitting the elimination of the skimmer heretofore required required at some intermediate stage of the evaporative concentration system and the feed of relatively soap-free liquor to the evaporators.

The novel features which are believed to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a complete pulp pro ducing system showing particularly those portions provided for the treatment of black liquor;

FIG. 2 is a schematic diagram showing a first modification of black liquor treatment portions of a system otherwise in accord with the system of FIG. 1;

FIG. 3 is a schematic diagram of a second modification of black liquor treatment portions of a system otherwise in accord with FIG. 1;

. FIG. 4 is a schematic diagram of a third modification of black liquor treatment portions of a system otherwise in accord with FIG. 1;

FIG. 5 is a schematic diagram of a complete pulp producing system incorporating the modification of FIG. 4 and showing a stock Washing arrangement diifering from that of FIG. 1; and

FIG. 6 is a diagrammatic elevation of a tank provided with a skimmer or separating partition which may be substituted for filtrate tanks, separating tanks or separating and soap storage tanks in any of the systems of FIGS. 1-5.

Referring now to FIG. 1, which shows diagrammatically the major portions of a system for paper fiber or pulp production including my invention, the southern pine wood chips are fed in the usual manner to a digester 1 for cooking, white cooking liquor and black liquor being introduced into the digester from a liquor measuring tank 2. After cooking, the pulp mass passes conventionally into a blow tank 3 where it is diluted with dilution black liquor introduced through pipe 4 and from the first stage filtrate tank 5. From blow tank 3, the mass may be passed through suitable defibering machines 6, which may be, for example, Jordan or Claflin units or the like. While not shown in the drawing, screens may be provided to follow the defibering step if desired to remove knots and other large pieces of wood or extraneous material. as is well known in the art. Before introduction of the fibrous mass into the first stage washer 7, the mass is preferably further diluted with black liquor supplied through pipe 8 from the filtrate tank 5.

The pulp, diluted with black liquor, passes into the first stage washer 7 through pipe 9 and a mass of fiber is sucked out of the fiber-containing liquor onto the revolving washing drum 10 and the fiber layer is carried under spray or shower heads 11. The washers indicated in the drawing are vacuum washing units wherein vacuum is maintained within the drum 10 by means of pipe 12 and the air and black liquor drawn into pipe 12 are supplied to the first stage filtrate tank 5. Vacuum on pipe 12 may be maintained by gravity or by suitable pumps (not shown), as may be desired, and the washers and washing system may be of a type generally similar to those shown and described in pages 504 to 512 and 771 to 775 of Pulp and Paper Manufacture, volume 1, Preparation and Treatment of Wood Pulp, 1950, The Maple Press Company, York, Pa. The washing system is preferably of the countercurrent or counter flow type and is arranged in the usual instance to supply through pipe 12 black liquor of about 16 to 18 percent solids content, i.e. the dry weight of solids is between 16 and 18 percent of the weight of the liquor. Black liquor from the first stage washer, and in the first stage filtrate tank, will be herein referred to as liquor of 17 percent solids content. My invention, however, is not dependent on any particular solids concentration and in certain systems it may be found practicable to operate in a manner to provide, liquor in the filtrate tank of as little as about 12 or 13 percent solids or as much as about 20 to 21 percent solids. My invention is substantially equally applicable to such systems regardless of the specific solids content of the liquor at the filtrate tank, and it will be recognized. that this invention does not pertain to the washing system itself.

The washing system shown comprises a second stage 13 having a suction line 14 and spray heads 15, a third stage 16 having suction line 17 and spray heads 18 and a fourth or final stage 19 having a suction line 20 and spray heads 21. The connections between the stages are such that hot water supplied to heads 21 of the final stage 19 is sucked out of the washing drum 22 by suction line 20 as black liquor having about 2 percent solids content and this relatively weak liquor is sprayed through heads 18 onto the pulp carried on the surface of washing drum 23 of stage 16. Solids washed from the pulp on drum 23, in turn, increase the solids content of the liquor sucked into line 17 to about 4 percent and this liquor is sprayed from heads 15 in the second stage 13 into the pulp on washing drum 24, there to extract more solids and to be drawn olf as liquor containing about 8 percent solids into line 14 for spraying from heads 11 of the first stage 7.

While the black liquor is thus being fed in a countercurrent direction, from the final washer stage to the preceding stages in inverse order, the fiber or pulp mass is being passed from the first stage 7, being collected from the surface of drum 10, into the next washer stage 13, and thence into stages 16 and 19. Upon removal from drum 22 of the finalstage, the pulp is collected in a brown stock chest 25 prior to the usual screening and refining steps. After screening and refining, the pulp passes to the Fourdrinier machine, these latter portions of the paper making process being merely exemplary and having no specific bearing on this invention.

The black liquor suction line 12 from the first stage washer extends into the first stage filtrate tank 5 and terminates at a level near the bottom of tank 5 and below the liquid level in the tank. The black liquor passing through line 12 carries entrapped air and a substantial concentration of fatty acid and resin soaps. The soaps and air, being of less specific gravity than the black liquor. tend to rise to the surface of the liquor, resulting in formation of foam above the liquid surface and in a relatively greater proportion of soap materials at and near the surface than in the lower portions of the tank. Since the dilution black liquor for mixing with the chips and pulp in the stages preceding the washers is desirably as soap-free as possible, the liquor for such dilution is withdrawn from the filtrate tank 5 through a conduit 26 opening into the tank at a level much lower than the liquid level and preierably at or near the bottom of the, tank as shown.

The filtrate tank. 5 is provided with additional means for removing the contents including one or more foam breakers 27 and one or more skimmers such as the skimming funnel 28. The skimming funnel 28 is disposed at the desired liquid level and opens upwardly in the tank, whereby the floating soap-rich materials fall into the funnel. A pump 29 is arranged to pump the materials from the skimming funnel into a second blank liquor separating tank 30.

It will be understood that the skimmer 28 need not be funnel-shaped but it may be an open-topped upstanding cylinder, or simply a weir in the side of the tank, or some other collector open to the foam and arranged to receive foam together with some soap-rich liquids and semiliquids from the liquid surface. Conveniently, the skimmer is ar ranged to permit liquid to spill over a rim or edge into the collector. It will be further understood that the position of the rim controls the liquid level in the filtrate tank,- and that as the level tends to rise above the level of the rim, surface liquid spills over into the skimmer or collector, thereby to establish and maintain the liquid level at, substantially, the level of the rims The liquid level established by funnel 28 in tank 5 is indicated by a broken line at 28'.

In normal operation of a pulp producing system of the type outlined above, and to which my invention is particularly applicable, the amount of black liquor used for cooking and dilution ahead of the washers constitutes a major portion of the black liquor received from the pulp Washers and may be between about and of the sesam first stage washer. Accordingly only a minor portion of the liquor received from the pulp washers is actually treated for the recovery of its chemical content. In other words, the rate of flow of black liquor from tank 5 through pipe 26 may be about eight to ten times by weight the rate of removal of materials by skimmer 28. While a substantial portion of the materials entering the funnel will be soap-r-ich liquor skimmed from the liquid surface, the funnel will also remove a portion of the foam which collects above the liquid level 28 particularly if the pump 29 is slightly oversize. Furthermore, :the broken foam return from foam breaker 27 is directed into the funnel and the broken foam is thus never mixed back into the liquids in tank'S but is furnished through the series of conduits into the second tank 30. If it is found more convenient, thebroken foam return pipe 31, which is shown as emptying'into funnel 28, may lead directly into tank 30. The usual vapor outlet 32 from foam breaker 27 may exhaust into the atmosphere.

The foam breaker return conduit 31 carries soap-rich black liquor which will contain an appreciable amount of entrapped air or fine foam, the exact amount of air and foam remaining depending uponthe efficiency of the foam breaker and upon the nature of the foam which passes to the foam breaker. Even the most eflicient modern foam breakers do not provide complete release of vapors or gases, and, in systems fed with resinous wood, such as southern pine, a substantial amount of soap materials are inherently present in the foam from black liquor.

The input to tank 30, accordingly, fromfoam breaker 27 will comprise a mixture of soap-rich black liquor with s'mallvapo-r bubbles entrained therein, a certain amount of .foam suckediinto the funnel 28, or spilling over into the funnel from above the liquid level in tank 5, and a substantial amount of soap-rich black liquor skimmed from the liquidlevel.

In addition to the materials from tank 5, including foam breaker 27, concentrated black liquor may be mixed with the liquids in tank 30 as later more fully explained. A ny concentrated black liquor so added may have a solids concentration of 45 or 50 percent, and in any event should have a solids concentration of substantially more than about 26 percent. &ifiicient concentrated black liquor is mixed, in accord with this preferred embodiment of my invention, with the liquids in tank 30 to increase the solids content to somewhat more than percent and preferably to between about 23 and 28 percent; Black liquor produced'in pulp systems of the type to which this invention pertains, for southern pine woods, has been found to have the llowest soap-entraining, or soap dissolving capacity at substantially 26 percent solids concentration. Thus liquor of 16 percent solids will hold several times the concentration or amount of soap held" in liquor of 26'percent solids.

, Black liquor is withdrawn from separation and storage tank by means of an outlet 33 positioned below the liquid level, and preferably at or near the bottom of tank 30 and supplied through a pipe or conduit 34 to an oxidation tower 35. It will be understood that a suitable pump may be inserted in conduit 34, as well as in other conduits throughout the system if desired, and when, for example, gravity flow is found insuflicient; Pumps will normally be found necessary at several parts of the system. A typical arrangement of pumps is shown although certain of these may be omitted and others provided and their locations will depend upon the relative elevation of the ends of the several conduits in the specific installation and by other variable factors. In the usual instance, pumps are required to withdraw foam and liquor mixtures from with a foam breaker 36 having a vapor outlet 37 exhaust ing into the atmosphere and a broken foam line or conduit 38 arranged to supply the broken foam prefer-ably connected through a suitable pump 40 to empty through.

conduit 41 into a settling tank or pit, into which, for example, conduit 42 may empty.

The disposal or further processing of broken foam from conduit 38 and of foam and soap-rich liquor from,

funnel 39 may be accomplished in any of several'difierout ways. Thus the materials from conduit 38 and from funnel 39 may be simply discarded, or one or the other may be discarded. be found desirable, for economic reasons and to reduce the amount of mill waste, to combine the materials by supplying the broken foam in conduit 38 directly into funnel 39, by supplying the broken foam from conduit 38 into the input line of pump 40 or, as shown in the drawing, by joining conduits 38 and 41 into a common conduit 42 which may then be directed into settling tank or pit.

, Black liquor may be extracted from the materials-thus supplied through conduit 42 and returned to the system, such as back into tank 30, while portions of the ma terial passing through conduit 42 may be used in the production of tall oil or for other purposes.

It will be understood that my invention is not particularly concerned with what disposal is made of the broken foam in line 38 or oflthe foam and soap-rich liquor drawn from the tank through funnel 39. The dispositions suggested above may be taken as merely typical of possible solutions to the disposalproblem. 'It will further be understood that it is not material to the invention whether the broken foam in conduit 38 is or is;

not mixed with the foam and soap-rich liquor extracted by theskimming funnel. If it is desired that they should be mixed, this may be accomplished by directing the conduit 38 to empty into funnel 39, in the same manner in which conduit 31 empties into funnel 28. Economics of all parts of the pulp mill are, however, interrelated,

and, if soap is to be discarded to waste, and if the geographic locality of the mill makes waste disposal expensive, it may be worthwhile to extract a maximum percentage of black liquor from the materials to be discarded. If tall oil is to be produced, it may be found desirable, in order to provide soap-rich materials most suited to tall oil production, to treat further the materials from one or another part of the system shown" as being directed together into conduit 42. l

It is important, however, in accord with the preferred embodiment of the system shown in FIG. 1, that the broken foam line from foam breaker 36 be not returned directly into tank 30.

Oxidation tower 35 may be of any of several types, such as the types shown in the above mentioned patents to Kress or Tomlinson.

Dependent to a considerable extent upon the concentration of the black liquor in tank 30 and upon the amount of soap which may be contained in any liquids furnished to the oxidation tower with the black liquor drawn from tank 39, more or less soap-rich surface liquids may accumulate and more or less foam may be produced in the oxidation tower 35. If necessary in the particular operating system, accordingly, a pump 43- may be arranged to draw foam and soap-rich liquor from the oxidation tower and to supply such foam and soap-rich materials to the settling tank with the materials of cork duit 42. Depending upon the design'of the oxidation tower and other factors, a skimming funnel may or may not be required within tower 35 to connect with pump 43.

Following oxidation of the black liquor in tower 35, the liquor is passed to a conventional chemical recovery system such as is commonly employed in kraft mill In most instances, however, it will operations and which provides means for evaporating the oxidized liquor, such as in multiple effect evaporators 44, as well as a system for recovering the chemicals contained in the concentrated black liquor obtained from the evaporators. The oxidized liquor from tower 35 is thus passed to multiple efiect evaporators 44 by means of pump 150 and line 151 wherein the oxidized black liquor is concentrated by evaporation and then passed to a concentrated black liquor storage tank, des ignated at 45, as by means of line 153. The concentrated. black liquor in storage tank 4-5 may be withdrawn for treatment in the concentrated black liquor recovery system, such as is generally indicated at 4-6, through pipe line 152, treated therein to produce white liquor in accord with methods well known in the art, and the white liquor passed to liquor measuring tank 2 through line 154.

In accord with the preferred embodiment of this invention, concentrated black liquor is also furnished from the storage tank 45 through conduit 47 back into separation and storage tank 30 for mixing with and increasing the solids content of the black liquor at this point, and prior to the furnishing of the black liquor to oxidation tower 35. As previously suggested, sufficient concentrated black liquor is so supplied to tank 30 as to increase the. solids content to approximately 26%, whereby the maximum amount of dissolved soap will become insolubilized and separate from the body of the liquor and may be removed at this stage. The recirculation through conduit 47 of the concentrated liquor greatly simplifies the problems which are associated. with the presence of soap in the various parts of the system, and makes unnecessary, for example, the provision of soapremoving means in the evaporator stage 44. In other words, the soap problem which exists in the normal system at several points in the system, is, in accord with this invention, concentrated in a single tank 39, and the problem can be satisfactorily handled at this one point.

In addition to serving as a tank from which soap and.

foam may be removed from the liquor passing through the system, tank 34 provides useful liquor storage in advance of the oxidation tower, and its presence permits an increased settling or breaking of the foam which is partially broken in foam breaker 27 of tank 5. The additional settling time which is given the liquor in tank 30 permits a more complete stratification of the foamrich materials toward the top of the liquid than would otherwise occur.

FIG. 2 discloses a portion of a system which may replace portions of the system of FIG. 1. For clarity and to prevent unnecessary duplication, only part of a complete system is shown, the omitted portions being otherwise like FIG. 1. The several elements of the system which may be identical as between the embodiment shown in FIG. 1 and the modification of FIG. 2 are identically numbered in the drawings, and the above description of these elements is, of course, applicable to FIG. 2.

The modified system of FIG. 2 differs from that of FIG. 1 in two important respects. In the first place, in FIG. 2, there is no provision for the supply of concentrated black liquor back from storage tank 45 into separation and storage tank 30, while an additional conduit is provided from near or at the bottom of first stage filtrate tank 5 into the oxidation tower.

In the system of FIG. 2, black liquor extracted in the first stage washer is introduced into filtrate tank 5 by conduit 12, as in FIG. 1, and black liquor is extracted from tank 5 through conduit 26 below the liquid level. Foam breaker 27 operates as in FIG. 1, supplying broken foam to tank 30 such as through conduit 31 and pump 29. Tank 30 acts as a storage and settling tank, and a bottom outlet, below the liquid level, connects through conduit 34 into the oxidation tower 35', the tower generally corresponding to that of FIG. 1. Additional black liquor, however, is extracted from well below the liquid level in tank 5 through a conduit 48 which empties 8" into the tower with the liquor from tank 30. Accordingly in the embodiment shown in FIG. 2, only a part of the liquor removed from tank 5 for subsequent treatment in the recovery system is withdrawn from filtrate tank 5 through skimmer funnel 28.

Broken foam from a foam breaker on tank 30, as indicated by conduit 38, together with soap-rich liquor and foam extracted by skimmer 39 and pump 40, is directed into a conduit 42 for disposition as desired.

The liquor received by tower 35' contains somewhat more soap than the liquor supplied to tower 35 of FIG. 1, and the liquor is somewhat less concentrated. Accordingly, greater foaming is to be expected in tower 35. However, the soap and foaming of liquor in tower 35 is substantially reduced from' what it might otherwise be, by the removal of soap, foam and soap-rich liquor, first, by the skimming action of skimmer 28 in tank 5, secondly by the removal of foam from tank 5' and furnishing'thereof' through conduit 31 directly into tank'30, where further settling occurs, thirdly, by the relatively slow removal of liquor from below the liquid level from each of two tanks, tanks 5 and 30, and finally by the skimming of soap-rich liquor and foam from tank 30 by means of skimmer 39 and conduit 38. The problem of foaming in the filtrate tank 5 is minimized in this manner, and

the foam breaker 27 does not'create mayonnaise" in tank 5, since the soap-rich liquid surface is skimmed and the soap-rich broken foam is removed and not returned into tank 5 for possible recirculation through the foam breaker. Accordingly, most of the most troublesome soap and foam problem is transferred into tank 30 and thereby largely isolated from the remainder of the system.

The soap problem in storage tank 30 is there handled by providing a relatively long settling time and by removing soap and soap-rich materials therefrom into a disposal system supplied by conduit 42.

If, as might be typical, approximately one-halfof the liquor supplied to tower 35 is extracted from tank 5 through conduit 48, the rate of flow from tank 30, through conduit 34 will be relatively small. Effective settling and floating off of soap-rich materials in tank 30 is accordingly permitted. The settling, becomes increasingly effective in tanks 5 and 30 as the rate of withdrawal of liquor therefrom is reduced. Since the materials supplied to tank 30 are more loaded with soap than the filtrate entering tank 5 through conduit 12, an appropriate feed for tower 35 might comprise approximately percent of liquor from tank 5 and 25 percent from tank 30. Some liquor is also being extracted from tank 5 through conduit 26, however, and such factors as the efficiency of foam breaker 27, the overall amount of soap in the filtrate, concentration of the black liquor, relative sizes of tanks 5 and 30, desired rate of flow into tower 35, and the type of disposal system supplied by conduit 42 may make desirable a different proportion of flow from the two tanks.

Since the liquor supplied to tower 35 in FIG. 2 will normally have a solids content of less than 26 percent, and more nearly 16 percent, and since some evaporativc concentration usually occurs during oxidation, and further since known economic oxidation towers inherently tend to produce foam, it is preferred in this system to skim. as by skimmer 49, foam and soap-rich liquor from the pool or tank of oxidized liquor in the lower end of the oxidation tower, or, in the separate collection or storage tank which may be connected to receive the oxidized liquor from the tower, the skimmed materials being pumped by pump 43 into conduit 42 of the. disposal system. For these reasons, too, it is likely to be necessary to provide a foam breaker 50 on the oxidation tower, exhausting gases therefrom to the atmosphere and passing the broken foam therefrom into the disposal system represented by conduit 42.

Oxidized black liquor from below the liquid surface of the pool receiving oxidized liquor is withdrawn as by pump 51 and supplied as in FIG. 1 to vacuum evaporators' 44 and thence to storage tank 45 and the concentrated black liquor recovery system indicated at 46. It is known to remove soap: during the evaporative concentration of liquor, and in the system of FIG. 2 it may become neces-: sary to employ a skimming soap removal step at some point in the concentrating sequence as suggested in the modification of FIG. 3.

' FIG. 3 shows a further modification of a system in which soap problems are transferred into equipment specially capable of handling the problem. It will be understood that in FIG. 3, as in FIG. 2 and as in FIG. 4 later discussed, only a portion of a complete system is shown and that omitted portions of the system are as shown in FIG. 1.

In FIG. 3, filtrate from the first stage washer is supplied through conduit 12 to tank 5, black liquor is withdrawn from tank 5 through conduit 26 and soap-rich liquor and foam and broken foam are withdrawn from tank 5 by means of skimming funnel 28, pump 29, foam breaker 27 and conduit 31, all as in FIG. 1. The materials thus withdrawn, however, in the system of FIG. 3, are supplied through conduit 5'2 to oxidation tower 135. A larger proportion of foam is produced in tower 135 than in the towers of the system above disclosed, and the foam at the top of the tower is permitted to flow over into an oxidizer tank 53, wherein the oxidation proceeds between the liquor and entrapped air such as through a large conduit 54. The oxidized liquor from tower 135, together with any foam and soap-rich materials which may be trapped with the liquor, are separately withdrawn by a pump 55 and associated conduits and supplied also to tank 53.

Since some concentration of liquor is accomplished in tower 135, the liquor supplied through pump 55 may have a higher percentage of solids than the liquor in tank 5 Furthermore, concentrated black liquor may be added through conduit 56 as later explained, whereby the percentage of solids in the oxidized liquor in tank 53 may be between about 17 and 20 percent.

Tank 5'3 is provided with a foam breaker 57, having a broken foam conduit 58 arranged to supply broken foam to skimming funnel 59. Skimmer 59 receives not only broken foam but also soap-rich materials and foam falling into the funnel from and above the liquid surface. These material are continuously separated from the body of the liquor prior to the completion of the oxidation step and are supplied through conduit 60 and pump 61 to a settling and soap removing tank 62. Valve 63 is provided in conduit 60 for purposes later explained.

Relatively soap-free liquor, that is, liquor from which has separated nearly all of the soap which will separate at the particular concentration of liquor, is withdrawn from tank 53, from a point well below the liquid surface therein by conduit 64 and pump 65 for supply to vacuum evaporators 44'. Following partial concentration, to about 28 to 32 percent solids in evaporator stage or stages 44', the liquor passes into a storage and separating tank 66, and liquor from well below the liquid level in tank 66 is supplied to an additional stage or stages 144 of the evaporator as desired, through conduit 67, and thence is directed into concentrated black liquor storage tank 45 as indicated.

The soap-rich liquor and broken foam from oxidizer tank 53 provided through conduit 60 is preferably mixed with foam and soap rich concentrated liquor drawn by a skimming funnel 68 from the liquid surface in storage and separating tank 66. These materials are supplied by pump 61 into one side or chamber 69 of auxiliary separating and storage tank 62. A partition or wall 70 extends across the tank dividing it into chamber 69 and chamber 71. The wall 70 terminates well below the top of the tank and permits foam and soap-rich surface liquor to fall over the top of the wall from chamber 69 into chamber 71, this action being in the nature of a skimming action. Chamber 71, in other words, acts like a large position to waste or to a tall oil plant or the like, and the pump is operated at a rate sufiicient to maintain a liquor or semi-solids level 73 in chamber 71 below the top of.

Wall 70, whereby surface accumulation in chamber 69 can spill over the top of the wall.

The liquor in chamber 69, which separates fromthe lighter soap-rich materials, and which accumulates toward the lower portion of chamber 69, has substantially greater solids content than the liquor in the first stage filtrate tank 5', because the soap-rich liquor extracted from tank 66 by skimmer 68 has been concentrated by evaporators,

44 to a typical solids content of between about 28 and 32 percent. system of FIG. 3, approximately one-quarter of the supply entering chamber 69 may come from funnel 68, and under such conditions, the liquor in the lower portion of chamber 69 may have approximately 19 to 22 percent solids content. This liquor is Withdrawn from chamber 69, with little entrained soap, through a conduit 74 into pump 75 and enters tank 53 through conduit 56. The liquor so returned to tank 53 being somewhat more concentrated than that in the filtrate tank 5, the returned liquor tends to raise the solids content or concentration of the liquor in tank 53, thereby to cause a greater separation of soap at this point. Some concentration of liquor, furthermore, normally accompanies the oxidation thereof in tower 135, and this further increases the solids content in the liquor of tank 53.

Valve 63 controlling the rate of withdrawal of soaprich materials from tank 53 and a valve 76 in conduit 77, controlling the rate of withdrawal of soap-rich materials and concentrated liquor from tank 66, are so adjusted as to provide optimum feedback of concentrated liquor in the portions of the system including tanks 53 and 62. As the liquor concentration in chamber 69 approaches 26 percent solids content, the separation of soap increases.' However, it may be unnecessary, in accomplishing the substantial isolation of the soap problem in tank 62, to feed back sufficient concentrated liquor to raise the solids content in chamber 69 beyond about 20 to 22 percent. The extent to which soap can be tolerated in the evaporators and in the recovery system in which white cooking liquor is prepared, and economics relating to the use or disposal of soap Withdrawn through pump 72, will bear upon the setting of valves 63 and 76, as will the sizes of tanks 53, 62 and 66, and the capacity of evaporative con centrators 44'.

In the system of FIG. 4, as in the systems of FIGS. 1 and 2, the soap problem'is for the most part isolated at a point in the system prior to the oxidation tower. As in' the system of FIG. 3, however, the system of FIG. 4 feeds back soap-rich, partially concentrated liquor and foam from a tank provided at an intermediate point in the evaporative concentration. As in each of FIGS. 2, 3 and 4, portions of the complete system are omitted and only so much of the system is shown as deviates from the system of FIG. 1.

The first stage filtrate tank'S as shownin FIG. 4 is provided with skimmer 28 through which broken foam and soap-rich liquor are withdrawn for supply to soap storage tank having a position and function somewhat similar to tank 30 of the system of FIG. 1. The construction of tank 130 corresponds generally to that of tank 62 of FIG. 3, and includes a wall 78 dividing the According to the preferred operation of the pos'a'l or tall oil facility. Relatively soap-free liquor accumulates in the lower portion of chamber 79 and is withdrawn therefrom by means of conduit 83 and pump 84. A portion of the liquor from pump 84 may be directed through a control valve 85 back into filtrate tank 5, while a second portion may flow through valve 86 into oxidation tower 135', corresponding generally to tower 35 of FIG. 1 or tower 35' of FIG. 2. A conduit 87 connecting near the bottom of tank is provided with pump 88 to supply preferably the major portion of the liquor received in tower 135'.

The system arranged as in FIG. 4 may operate so as to provide liquor in chamber 79 of about 18 or 19 to about 22 or 23 percent solids concentration, whereby the liquor furnished back through valve 85 tends to raise the concentration of liquor therein, and being itself low in soap, tends to reduce the soap problem in the filtrate tank. At the same time, the admixture of the relatively soapfree liquor through valve 86 with the somewhat less concentrated liquor from conduit 87 diminishes the soap problem in the oxidation tower and in the evaporators 44'.

The system of FIG. 5 embodies the modification of FIG. 4, and shows a modification of the FIG. 1 system involving primarily the stock washer stages. In FIG. 5, each of the stock washer stages is provided with a filtrate tank which is vented into the first stage filtrate tank.

More particularly, filtrate tank 20" of the fourth and final washer stage 19' receives liquor through conduit 120 from the washer drum, hot water being sprayed by system 21 through the pulp as in the usual Washer system. Liquor is pumped from tank 20 into spray system 18 of. the next preceding stage 16', and from its filtrate tank 17" into spray system 15' of stage 13', and from tank 14 of the second stage 13' into spray system 11' of the first stage 7. As in the previously described systems, conduit 12 supplies black liquor from stage 7 into the first stage filtrate tank 5.

Each of the filtrate tanks. 20', 17" and 14" is provided with a respective venting conduit 89, 90, 91, of sutiicient size freely to pass foam, and each conduit connects, as through header 92, into tank 5.

The venting of each filtrate tank into the first stage filtrate tank very largely removes the soap and resultant foaming problems from the stock washing system and these problems are minimized in tank 5' and isolated in tank 130 by the remainder of the system, which, as in FIG. 4, comprises a feed-back partially concentrated liquor connection from funnel 68 of tank 66 into chamber 79, and a soap-rich liquor and foam withdrawal through skimmer 23 of tank 5, also added to chamber 79. Relatively soap-free liquor is drawn from chamber 79 by pump 84 and supplied back to tank '5' through valve 85 and to oxidation tower 135 through valve 86. Black liquor is also supplied to tower 135 directly from tank 5' through pump 88, a valve 93 being shown for regulating the flow in conduit 87. Liquor from oxidation tower 135 is thereafter supplied to the chemical recovery system, the liquor first passing to the system by way of pump 15% and line 151 to evaporators 44. The partially concentrated liquor in tank 66 is furnished as necessary to additional concentrator units 144 and thence to the concentrated black liquor storage and recovery system 45'. The operation of the last mentioned portions, and of other portions of the system correspond to operation previously set forth for components identified with like numerals.

It will be recognized that the system following the first stage filtrate tank of FIG. 5 is in accord with the modification of FIG. 4. FIG. 5 discloses primarily a modification in the stock washing system, in which the filtrate tank for each washer stage is vented into the first stage filtrate tank to permit foam to pass from each filtrate tank of the second, third and fourth stages directly into the first stage filtrate tank. This modification is intended to 12 be applicable in systems otherwise in accord with any one of FIGS. 1, 2 or 3 hereof.

It is believed apparent that more or less than four washer stages may be employed in a stock washer system as dictated by considerations not directly concerned in this invention, the inclusion of four stages being exemplary only. It is also believed apparent that one or more vents, such as vent 89 for the filtrate tank of the final washer stage, may be omitted if it should be found that only a very small amount of foam occurs in the filtrate tank involved. Particular advantages of the venting system of FIG. 5 lie in the possibility of using substantially smaller pumps, such as pump 15", to provide washing liquor, as from tank 17" to spray heads 15, since such pumps in accord with this modification are not required to pump foam as well as liquor, and in the substantial reduction of soap accumulation in the several tanks, spray heads and conduits, and in and on other parts in the washer system. As hereinabove explained, pumps and valves may be included at various points in the illustrated systems as necessary and as is well known in the art, and as is known, pumps are usually employed to furnish liquor from each filtrate tank to the spray heads of the next preceding washer stage. Alternatively, however, the filtrate tanks may be mounted above the spray heads and supplied with filtrate washing liquor by pumping from the drum connection, gravity flow being relied upon to supply the spray heads. While pumps are usually required to move skimmed materials, and while pumps are shown at positions in the systems described where, in general, soap-rich, foamy materials are involved, the particular flow at these and other points may be obtainable by gravity, while at other points, where pumps are not shown, pumps may be found necessary.

FIG. 6 is a representation of a separating tank 94 having therein a modified skimmer. A tank of this design may be substituted for any one of the first stage filtrate tanks 5 or 5 of any of the described systems, or for any of the tanks 30, 53, 62, 130 or 66 of the described systems, subject only to obvious modification in the number of connections or the like.

In tank 94, a preferably centrally disposed open top cylinder 95 acts in much the same manner as the skimming funnels or partition walls of the tank which it may replace. An inlet pipe is represented at 12" through which liquor, broken foam, foam, soap-rich liquor or the like may enter the tank, collecting to the level 96 in a chamber 97 surrounding the central cylinder. As the level increases above the upper edge of the cylinder, the floating surface layer falls over into chamber 98 within the cylinder. These materials are withdrawn by means of conduit 99 and pump 100. The broken foam line 101 from foam breaker 102 may also deposit soaprich materials into chamber 98. A conduit 103 is shown communicating with the lower portion of chamber 97 for removing, for example, black liquor settling below upper soap-rich layers. Conduit 103, accordingly, corresponds to conduit 26, 34, 64 or 83 of the herein described systems, and it will be understood that additional conduits may be provided to correspond to conduits such as conduits 54 and 56 of FIG. 3, or the conduit connecting pump 81 and tank of FIG. 4, or the like, as required.

While only certain preferred embodiments of this invention have been shown and described by way of illustration, many modifications will occur to those skilledin the art and it is, therefore, desired that it is understood that it is intended in the appended claims to cover all such modifications as fall within the true spirit and scope of this invention.

What is claimed as new and what it is desired to secure by Letters Patent of the United States is:

1. In the sulfate process for producing paper pulp from resinous wood wherein the black liquor as received from the pulp washers is accompanied by entrained insoluble soap and entrapped air which cause foaming and clogging of equipment and wherein a major portion of the black liquor received from the pulp washers is recycled as dilution liquor and a minor portion of the black liquor received from the pulp washers is thereafter oxidized and subsequently treated in a chemical recovery system in which the oxidized liquor is subjected to processing steps which include the concentration of the oxidized liquor by evaporation and the burning of the concentrated liquor in a furnace,

the improved method of handling and treating the black liquor prior to the recycle of said major portion as dilution liquor and prior to the treatment of said minor portion in said recovery system comprising continuously collecting the black liquor from the pulp washers in a tank in which the accompanying insoluble soap floats to the surface of the collected liquor in said tank and the entrapped air forms foam above said surface,

continuously withdrawing a portion of said collected liquor from said tank for recycle as said dilution liquor, the withdrawn portion being removed from below the surface of the collected liquor in said tank and thereby being relatively free of insoluble soap and foam,

continuously withdrawing another portion of said collected liquor from said tank and thereafter oxidizing the withdrawn other portion in an oxidation tower by therein contacting said withdrawn other portion with air, said other portion of said collected liquor constituting at least a part of said minor portion and being withdrawn from said tank by skimming black liquor from the sur face of the collected liquor in said tank, thereby simultaneously withdrawing said insoluble floating soap from the surface of the collected liquor together with said other portion,

continuously removing the foam from said tank and breaking the removed foam in a foam breaker to produce a liquid phase which includes partially broken foam,

continuously collecting said liquid phase and said other portion together with the withdrawn insoluble floating soap in another tank in which the withdrawn insoluble floating soap and partially broken foam float at the surface of the black liquor collected in said other tank,

continuously skimming the withdrawn floating insoluble soap and partially broken foam from the surface of the black liquor collected in said other tank and disposing of the skimmed insoluble soap and partially broken foam from said other tank externally of said recovery system,

continuously withdrawing black liquor from below the surface of the black liquor collected in said other tank, and thereafter passing the black liquor withdrawn from said other tank to said recovery system.

2. The improved method according to claim 1 further 14 comprising continuously feeding concentrated black liquor from the recovery system to the collected black liquor in said other tank to form a mixed liquor of increased solids content in said other tank and thereby to insolubilize soap dissolved in said collected black liquor and to increase the amount of insoluble soap at the surface of said mixed liquor in said other tank, and passing the black liquor withdrawn from the said other tank to said oxidation tower prior to the said passing thereof to said recovery system.

3. The improved method according to claim 1 further comprising continuously feeding concentrated black liquor from the recovery system to the collected black liquor in said other tank to form a mixed liquor of increased solids content in said other tank and thereby to insolubilize soap dissolved in said collected black liquor and to increase the amount of insoluble soap at the surface of said mixed liquor in said other tank, and passing the black liquor withdrawn from the said other tank to said oxidation tower prior to the said passing thereof to said recovery system, and wherein said collected black liquor in the first mentioned tank has a solids content from about 15% to 18% solids, said concentrated black liquor has a solids content substantially in excess of 26% solids and said mixed liquor has a solids content from about 23% to 28% solids.

4. The improved method according to claim 1 wherein the said oxidizing of the withdrawn other portion by contact with air in said oxidzation tower precedes the said collecting of said other portion in said other tank.

5. The improved method according to claim 1 wherein the said oxidizing of the withdrawn other portion put in by contact with air in said oxidation tower precedes the said collecting of said other portion in said other tank, and further comprises continuously feeding concentrated black liquor fromthe recovery system to the collected black liquor in said other tank to form a mixed liquor of increased solids content in said other tank and thereby to insolubilize soap dissolved in said collected black liquor and to increase the amount of insoluble soap at the surface of said mixed liquor in said other tank.

References Cited in the file of this patent UNITED STATES PATENTS Tomlinson et al. Apr. 22, 

1. IN THE SULFATE PROCESS FOR PRODUCING PAPER PULP FROM RESINOUS WOOD WHEREIN THE BLACK LIQUOR AS RECEIVED FROM THE PULP WASHERS IS ACCOMPANIED BY ENTRAINED INSOLUBLE SOAP AND ENTRAPPED AIR WHICH CAUSE FOAMING AND CLOGGING OF EQUIPMENT AND WHEREIN A MAJOR PORTION OF THE BLACK LIQUOR RECEIVED FROM THE PULP WASHERS IS RECYCLED AS DILUTION LIQUOR AND A MINOR PORTION OF THE BLACK LIQUOR RECEIVED FROM THE PULP WASHERS IS THEREAFTER OXIDIZED AND SUBSEQUENTLY TREATED IN A CHEMICAL RECOVERY SYSTEM IN WHICH THE OXIDIZED LIQUOR IS SUBJECTED TO PROCESSING STEPS WHICH INCLUDE THE CONCENTRATION OF THE OXIDIZED STEPS WHICH INCLUDE THE CONCENTRATION OF THE OXIDIZED LIQUOR BY EVAPORATION AND THE BURNING OF THE CONCENTRATED LIQUOR IN A FURNACE, THE IMPROVED METHOD OF HANDLING AND TREATING THE BLACK LIQUOR PRIOR TO THE RECYCLE OF SAID MAJOR PORTION AS DILUTION LIQUOR AND PRIOR TO THE TREATMENT OF SAID MINOR PORTION IN SAID RECOVERY SYSTEM COMPRISING CONTINUOUSLY WITHDRAWING A PORTION OF SAID COLLECTED LIQUOR FROM SAID TANK FOR RECYCLE AS SAID DILUTION LIQUOR THE WITHDRAWN PORTION BEING REMOVED FROM BELOW THE SURFACE OF THE COLLECTED LIQUOR IN SAID TANK AND THEREBY BEING RELATIVELY FREE OF INSOLUBLE SOAP AND FOAM, CONTINOUSLY WITHDRAWING ANOTHER PORTION OF SAID COLLECTED LIQUOR FROM SAID TANK AND THEREAFTER OXIDIZING THE WITHDRAWN OTHER PORTION IN AN OXIDATION TOWER BY THEREIN CONTACTING SAID WITHDRAWN OTHER PORTION WITH AIR, SAID OTHER PORTION OF SAID COLLECTED LIQUOR CONSTITUTING AT LEAST A PART OF SAID MINOR PORTION AND BEING WITHDRAWN 